Structural chromosome aberrations

chromosomal aberrations

1. Wel come Topic :- structural Chromosomes aberrations and there role in plant breeding presented by, shrishaila PG14AGR6066 UAS Raichur 1 UASR shri cd

2. Variation in chromosome structure or number is called chromosomal aberration 2 UASR shri cd

3. Chromosome Structural aberrations The chromosome aberrations in which they alters the structure of chromosome(sequence of genes or kind of genes in chromosome or no. of genes) There are mainly four types which are Changes in the numbers of genes Deletion/Deficiency Duplication Changes in the location of genes Inversions :- 180 o rotation Translocations:- Exchange 3 UASR shri cd

4. Origin of structural aberrations Deletion spontaneously or may induced Mis -division of the centromere radiation, UV, chemicals, viruses may increase breakage Duplication Unequal crossing over Crossing over in inversion heterozygotes Crossing over in translocated heterozygotes 4 UASR shri cd

5. Inversion Spontaneously and induced Naturally in Drosophila Produced through breakage and reassociation of chromosome Translocation Spontaneously Induced by mutagens Growing a plants in ca deficit medium 5 UASR shri cd

6. Deletion First chromosome aberration discovered by the Bridges in 1917 in Drosophila Usually detected by based on unpaired region of normal chromosome produces a loop during pachytene stage Two types which are Terminal Intercalary 6 UASR shri cd

7. Deletions Loss of a (generally small) segment of chromosome A B C D E F G A B D E F G C 7 UASR shri cd

8. Terminal deletion Loss of segment contain a telomere of affected chromosome In 1938 M uller postulated that loss of telomere makes chromosome unstable so it is not commonly observed Ex: maize 8 UASR shri cd

9. Intercalary deletion Loss of segment in between centromere and telomere It is commonly observed Ex:Drosophila 9 UASR shri cd

10. Effects of deletion Pseudo dominance Crossing over not there Harmful effect on diploid organisms Most are as recessive Lethals Morphological effects 10 UASR shri cd

11. Duplication Bridges in 1919 It is detected by presence of loop formation during pachytene stage in duplicated region or cross pairing between segments of non- homologus chromosomes 11 UASR shri cd

12. Duplications It is type of structural aberration in which resulting the doubling of the segment A B C D E F G A B C D E F F G 12 UASR shri cd

13. Mainly four types Tandem Intrachomosomal Reverse tandem Displaced Translocated Interchromosomal 13 UASR shri cd

14. Effects of duplicatio n According to Ohno (1970) origin of new genes mainly due to duplication resulted the evolution Position effect Ex: Bar eye is result of duplication of 16A region of X chromosome of Drosophila Activity of certain enzymes may be doubled Ex:chromosome 6 of barley increased the activity of α -amylase ( hagberg in 1965) 14 UASR shri cd

15. 15 UASR shri cd

16. Inversion Sturtevant & punnet in 1921 in Drosophila Detected by presence of partial male sterility comparing with the normal strain by using linkage map presence of inversion loop during pachytene absence of crossing over. 16 UASR shri cd

17. Inversions It is the structural aberration in which the change in the sequence of chromosomal arrangement 180 o reversal of chromosome segment A B C D E F G H I J K A B C H G F E D I J K 180 O 17 UASR shri cd

18. Types of inversion Paracentric :- inverted segment does not include centromere and confined to one arm Pericentric :- included the centromere 18 UASR shri cd

19. Effects of inversion Partial male sterility Formation of Recessive mutation Position effect Effects the activity of the NOR of complement chromosome move active genes to sites generally inactive; lose gene function and vice versa 19 UASR shri cd

20. Translocations It is a type of structural chromosome in which change in position of the segment in such that they become integrated into same or homologous or non homologous chromosome Detected by formation of cross shaped configuration at pachytene between two non homologous chromosomes Ring of 4 chromosomes at metaphase 1 due to pairing between homologous chromosomes 20 UASR shri cd

21. Translocations Exchange of segments between non-homologous chromosomes F A B C D E L M N O P Q 21 UASR shri cd

22. Types of translocations Based on involment of chromosome Intrachromosomal Intraradial:-shift occur in same arm Extraradial :-shift occur in different arm Interchromosomal fraternal:-shift occur to homologous chromosome External:-shift occur to non homologous chromosome 22 UASR shri cd

23. Based on number of breaks involved Simple It involves one break terminal segment of chromosome integrated at the one end of non homologous chromosome R eported by painter and muller in 1929 in Drosophila 23 UASR shri cd

24. Shift translocation It requires three breaks Intercalary segment of a chromosome is integrated within a non homologous chromosomes Commonly seen in Drosophila , Neurospora 24 UASR shri cd

25. Reciprocal translocations It requires one break in each of the chromosomes Segments will exchanged between non homologous chromosomes Designated by prefix ‘T’ 25 UASR shri cd

26. Effects of translocations Alters the chromosome morphology Position effect Damage to DNA may result in formation of recessive lethals Lead to impaired fertility complications to synopsis and segregation 26 UASR shri cd

27. Uses of structural aberration Study of chromosome pairing and its behaviour during cell division For locating genes on particular chromosome To resolve special problems such as relation between chaisma and crossing over Used in plant breeding by increasing the dosage of certain desirable genes for increasing the activity 27 UASR shri cd

28. Continue... Homozygous duplication in heterozygous condition will gives the permanent hybrid vigour Useful in study of position effect New genes can be produced only through duplications Paracentric inversion will used to produce acentric fragments intact 28 UASR shri cd

29. Cont.... Used to study the specific problems in genetics Ex:-C1B Technique by muller in Drosophila C:-Inversion 1:-1 Recessive lethal B:-Bar eye Important role in evolution Desirable characters can be detected using inversion Translocation used in determination of unknown locus of gene and chromosome mapping Testing the association between linkage groups Used to know the point of intiation of chromosome pairing Production of duplication Evolution of allopolyploidy 29 UASR shri cd

30. Effects on humans Deletions in Humans Cri-du-chat syndrome Micro deletion of chromosome 5 DiGeorge syndrome Micro deletion of chromosome 22 Angelman syndrome Micro deletion of chromosome 15 30 UASR shri cd

31. Translocations Several human cancers are associated with reciprocal translocations Chronic myelocytic leukemia Burkitt’s lymphoma The Philadelphia Chromosome Reciprocal translocation between chr . 22 and chr . 9 31 UASR shri cd

32. T...................U 32 UASR shri cd